My elderly mother is unable to reach the chain to operate her blinds, so I made RoboBlinds !

It is battery powered and remote controlled.

She lives an hour away so battery life is important as she has to leave it to me change them.

I 3D printed the box and the gear wheel.

Step 1: Problem 1 - the Chain Link

I was unable to move the chain link because the drive wheel was inaccessible, in the very corner of the window bay.

I had to make the gear wheel move up (& down) and be wide enough to compensate for chain link !

I needed a spring to push the drive back down but I didnt have one small enough or much room, so I used two magnets (image 3) repelling each other.

As can be seen in the video, this works a treat !

The shape of the gear is also important, see the 3D print step.

Step 2: Problem 2

Battery drain.

I built this a few months ago so I am not too sure of the current draw but if memory serves me correct, in idle state, the control board draws about 30mA. With the batteries in series, theoretically this gives approx 2 weeks before the batteries need changing. Real world, I'm guessing a week.

The remote reciever only draws about 3mA on stand by, a big difference !

To overcome the problem, I used a self latching relay ! These are great as they have 2 coils, 1 to set the relay & another to reset the relay, just a quick pulse so there is no holding current ! I purchased them from RS online.

Image 2 shows the DC to DC buck converter. This is required as I use the 2 batteries in series, so when fully charged, they supply about 8 volts - enough to fry the remote receiver!

The circuit is very straight forward see Circuit Diagram step.

Step 3: The Circuit

The circuit is relatively straight forward.

The two batteries feed the buck converter which supplies the 5v to the remote receiver.

The supply voltage to the motor control board is fed via the relay. The 5v for the flashing LED is also fed via the relay so only the remote reciever (and the two transistors) have a constant supply.

The remote transmitter has 4 buttons and the receiver 4 corresponding outputs.

The output pin order is not logical ! This is why my button B turns the relay on and A turns it off !

When turned on, the LED flashes as a reminder to switch the device off in order to save power.

The output of the receiver is not high enough to pulse the relay so I used a couple of transistors to give it a boost.

Pretty much any NPN transistor will suffice. There are no biasing or current limiting resistors for the transistors as they are only on for a second or so while the transmit button is pressed.

Buttons C & D control the direction of the motor. The output of the receiver is enough to select the direction without the need for a transistor.

Step 4: 3D Prints

I printed the box in 2 halves and used M3 brass thread inserts to screw them together.

The drive cog was printed in 2 halves and superglued together. Note the flange to the outer rims. This is to allow the larger chain link to pass through without a problem.

I ran out of white filament which is why the box is two tone !